Skirted main metering jet for a carburetor

ABSTRACT

The main metering jet in a carburetor for an internal combustion engine includes a cylindrical skirt depending below the intersection between the main fuel jet passage in which the main metering jet is disposed and the main fuel well passage leading to the carburetor mixture conduit. The skirt establishes a uniform turning point for the fuel from the jet irrespective of the angular manufacturing variations in the intersection of the two passages.

Unite Wentis 1 Dec. 3 1974 [54] smnTEn MAIN METEmNo JET FOR A 2,969,9651/1961 B11111 2111/11 1 R C R T 3,361,416 1/1968 Morgan ct al 1. 261/69R 3,549,133 12/1970 Frankowski et al. 261/51 [75] Inventor: George W.Wentis, Rochester, NY. [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Jan. 111, 1973 21 Appl. No: 322,711

52] us. c1. 261/51 [51] int. Cl. lFtl2m 7/22 [58] Field of Search261/51, 34 R, 34 A, 69 R [56] References Cited UNITED STATES PATENTS2,261,794 11/1941 Carlson et a1..1..j 2151/51 2,615,695 10/1952 Winkler261/34 A 2,964,303 12/1960 Smith et al 261/51 Primary ExaminerTim R1Miles Attorney, Agent, or Firm-Peter D. Sachtjen 5 7] ABSTRACT The mainmetering jet in a carburetor for an internal combustion engine includesa cylindrical skirt depending below the intersection between the mainfuel jet passage in which the main metering jet is disposed and the mainfuel well passage leading to the carburetor mixture conduit. The skirtestablishes a uniform turning point for the fuel from the jetirrespective of the angular manufacturing variations in the intersectionof the two passages.

1 Claim, 3 Drawing Figures SlltllltTIED MAll N METERING .IlET FOR ACARBURIETGR The present invention relates to carburetors for internalcombustion-engines and, in particular, to the main metering system forthe delivering of fuel to the carburetor mixture conduit.

Current carburetors include a main fuel delivery system comprising avertical passage leading from the fuel bowl which is intersected by anangularly disposed drilled passage discharging at the venturi section ofthe carburetor mixture conduit. Ametering jet is disposed in thevertical passage. A throttle actuated metering rod controls the flow offuel through the jet. Accurate metering of the fuel is necessary forproper operation of the system. It has been found that this meteringcapability is adversely affected by the tolerances incident to theintersection of the two passages.

In conventional systems, the main metering jet discharges above theintersection of the two passages. Due to the permissible angularvariations in drilling the second passage, the axial location of theedge of the inlet to the second passage can vary considerably withrespect to the jet. This has been found to cause large meteringvariations between carburetors in production. While it is not completelyunderstood why this occurs, it is thought that the varying location ofthe intersection between the passages changes the turning point and thusthe metering of the fuel between the jet passage and the angular fuelwell passage.

The present invention provides a main metering jet construction whichprovides a uniform turning point for the fuel at the transition betweenthe jet passage and the fuel well passage. This is achieved by includinga depending cylindrical skirt at the discharge of the main metering jet.The lower edge of the skirt extends below the intersection of the twopassages within the range of production tolerances for drilling the fuelwell passage. Thus regardless of the actual position of theintersection,the skirt will extend into the projected envelope of the fuel wellpassage and will provide a fuel turning point interior thereof. Testinghas shown that this construction provides accurate metering of the fuelirrespective of the aforementioned tolerances.

These and other features of the present invention will be apparent toone skilled in the art upon reading the following detailed description,reference being made to the accompanying drawings showing a preferredembodiment in which:

FIG. l is a partial cross sectional view of a carburetor having a fuelsupply system including a skirted main metering jet with metering rodremoved made in accor dance with the present invention;

FIG. 2 is a view taken along line 22 ofFIG. ll showing the position ofthe main metering jet with respect to the intersection between thepassages.

FIG. 3 is a schematic view illustrating the effect of drillingtolerances on the location of the intersection between the passages.Referring to the drawings, there is shown a carbure tor 110 having a.vertical mixture conduit 12 for downwardly delivering a mixture ,of fueland air to an internal combustion engine as controlled by the openingand closing of a throttle valve 14. The mixture conduit li2 includes aconventional main venturi l6. Conventional first and second boostventuriis l8, W are disposed in the mixture conduit 112.

The carburetor it) further includes a covered fuel bowl 20. The supplyof fuel entering the fuel bowl 20 is controlled by a float mechanism notshown.

The main fuel supply system for delivering fuel from the bowl 20 to themixture conduit 12 includes a vertical main fuel jet passage 24, a mainmetering jet 26 disposed in the jet passage 24, and an angularlydisposed fuel well passage 28 extending from the jet passage 24 to theboost venturi l8, and a main discharge fuel nozzle 36 disposed in theupper end of the well passage 26.

The jet passage 24 is drilled vertically from the lower surface of thefuel bowl 20. The jet passage 24 includes an upper counterbore 32 havingan accurately machined annular seating surface 34, an intermediatethreaded section 36, and a lower cylindrical bore 36.

The well fuel passage 28 is drilled from the boost venturi l8 andangularly intersects the passage 24 at an elliptical inlet 40. Anenlarged counterbore 42 is formed at the upper end of the well passage28 adjacent the upper boost venturi 18.

The fuel discharge nozzle 30 is .a conventional tubu lar construction.The nozzle includes an enlarged cylindrical section 44 which is pressedinto the counterbore 42 to locate the nozzle 30 in the mixture conduit12. The discharge nozzle 30 includes a downwardly directed dischargeopening 46 and. an upper air bleed passage 47. A vertical air bleedpassage 46 intersects the well passage 28 below the nozzle 30. An airbleed cap 50 including an orifice 52 regulates the air bleed through thepassage 48.

The main metering jet 26 includes an upper circular head section 60, anintermediate threaded shank 62, and a depending cylindrical skirt 64.The head section includes a lower annular seating surface which engagesthe seating surface 34 of the counterbore 32. When the threaded shank 62is threadably disposed in the threaded section 36 of the jet passage 24the skirt 64 depends downwardly into the bore 36. v

The main metering jet 26 includes an axially disposed fuel meteringpassage comprising an upper bore '70, an intermediate restrictedmetering orifice 72, and a lower discharge bore 74. As shown in FlG. 2,a tapered metering rod 78 actuated by the carburetor throttle linkage(not shown) controls the flow of fuel through the jet 26. x

In operation, as the throttle valve 14 is opened the resulting pressuredrop at the venturi 116 draws fuel from the bowl 20 through the jet 26into the passage 24. The fuel then is drawn upwardly in the well passage28, mixed with air from the air bleed passages 47, 46 and dischargedfrom the opening 46 into the mixture conduit 12 for delivery to theengine.

However, it has been found that the fuel metering to x the conduit 12can be affected by the geometry of the fuel supply system and, inparticular, the location of the inlet 40 with respect to the jet 26. Asshown in FIG. 3, the well passage has a nominal axis 60. Due to normalproduction tolerances incident to the drilling of the passage 28, theactual axis will be located with a tolerance cone 82, typicallyhaving'an included angle of around 2. This causes the opening; 46 andthe jet pas sage 24 to vary axially with respect to the axis of the jetpassage 24. For a 2.5 inch passage 26, the axial variation is around0.090 inch. Absent the skirt 64, it is thought this results in a varyingturning point for the 3 fuel flowing between the passages 24, 28 andaffects the metering fuel in the system.

The cylindrical skirt 64 of the present invention extends below theupper edge of the opening 40 for all tolerances incident to thedrilling. In other words, the lower rim of the skirt 64 projectsinterior of the projected cylindrical envelope of the well passage 28.For a 0.170 inch diameter well passage 28 and the above angulartolerances, a penetration of the envelope of at least 0.020 is thoughtto be desirable. Inasmuch as the rim and the opening 40 can beaccurately located with respect to the surface 34,.the easily obtainedaccurate referencing the skirt 64 to the seating surface of the headsection 60 will ensure a uniform turning point for the fuel irrespectiveof the angular tolerances. This in turn has been found to provideaccurate fuel metering despite manufacturing variations in the geometryof the fuel passage.

Although only one form of this invention has been shown and described,other forms will be readily apparent to those skilled in the art.Therefore, it is not intended to limit the scope of this invention bythe embodiment selected for the purpose of this disclosure but only bythe claims which follow.

What is claimed is:

l. A carburetor for an internal combustion engine comprising: a mixtureconduit; a fuel supply; a fuel metering system interconnecting said fuelsupply and said mixture conduit including a first downwardly extendingvertical passage communicating with said fuel supply; an annular seatingsurface surrounding said vertical passage; a second passage in said fuelmetering system angularly disposed with respect to said first passage,said second passage having an outlet at said mixture conduit and aninlet at said first passage, said inlet being variably axially disposedwithin a predetermined tolerance of said seating surface; a metering jethaving a shank section disposed on said first bore and a head sectionhaving a fiat annular surface adjacent the shank section seated againstsaid seating surface; a cylindrical skirt on said shank section, saidskirt having a diameter smaller than said shank section, extendingsubstantially below said shank section, and terminating with a lower rimspaced a predetermined distance from said flat annular surface of saidhead section, said predetermined distance being sufficient to ensurethat said rim extends axially below the edge of said inlet of saidsecond passage for all locations of said inlet within said predeterminedtolerance to ensure that fuel is discharged at said skirt interior ofthe projected envelope of said second passage thereby defining a uniformturning point for fuel passing from said jet to said second passageirrespective of the relative locations of said passages.

1. A carburetor for an internal combustion engine comprising: a mixtureconduit; a fuel supply; a fuel metering system interconnecting said fuelsupply and said mixture conduit including a first downwardly extendingvertical passage communicating with said fuel supply; an annular seatingsurface surrounding said vertical passage; a second passage in said fuelmetering system angularly disposed with respect to said first passage,said second passage having an outlet at said mixture conduit and aninlet at said first passage, said inlet being variably axially disposedwithin a predetermined tolerance of said seating surface; a metering jethaving a shank section disposed on said first bore and a head sectionhaving a flat annular surface adjacent the shank section seated againstsaid seating surface; a cylindrical skirt on said shank section, saidskirt having a diameter smaller than said shank section, extendingsubstantially below said shank section, and terminating with a lower rimspaced a predetermined distance from said flat annular surface of saidhead section, said predetermined distance being sufficient to ensurethat said rim extends axially below the edge of said inlet of saidsecond passage for all locations of said inlet within said predeterminedtolerance to ensure that fuel is discharged at said skirt interior ofthe projected envelope of said second passage thereby defining a uniformturning point for fuel passing from said jet to said second passageirrespective of the relative locations of said passages.